1. Field of the Invention
Embodiments of the invention relate generally to an error correction method. More particularly, embodiments of the invention relate to an error correction method capable of correcting single occurrences of predetermined error patterns.
2. Description of Related Art
Error detection and correction techniques play an important role in a variety of communication systems where data is transmitted across noisy communication channels. As the data is transmitted across the noisy channels, it may become corrupted. However, the error detection and correction techniques allow the data to be restored to its original uncorrupted state.
Most error detection and correction techniques involve transmitting some form of redundant data across a communication channel together with a data payload. For example, redundant data such as a parity bit or a checksum may be combined with data to be transmitted, and then subsequently used to detect and correct errors in the data.
One common technique used for error detection and correction is cyclic redundancy check (CRC). In this technique, data to be transmitted is modified by a generator polynomial to form a codeword. Here, the term codeword should be interpreted broadly to refer to data that has been modified to form a code. The length of a codeword can vary, and a codeword may include multiple cycles of a cyclic code. The term “transmitted codeword” will be used to refer to a codeword before it is decoded by a receiving device, and the term “detected codeword” will be used to refer to a codeword after it has decoded by a receiving device. Since errors can be introduced into the transmitted codeword during transmission, the transmitted codeword before transmission may be different from the detected codeword.
A given communication channel often tends to produce errors in specific patterns. Such patterns can often be discovered, for example, through observation, or from a priori knowledge of the channel's characteristics. Because the errors tend to occur in specific patterns, error correction techniques can take advantage of the known error patterns for a particular channel to determine how to best detect and correct the error patterns.
One example of how known error patterns can be used in error correction is to compute an estimated error signal for a detected codeword and then correlate the estimated error with the known error patterns. When this technique is successful, it produces an error pattern and a start position of the error pattern within the detected codeword.
The estimated error signal used in the above technique is typically computed as a difference between an equalized sequence and a convolution of the detected codeword and an equalizer target response. The detected codeword is typically generated by performing a Viterbi-decoding operation on the equalized sequence, and the equalizer target response is a partial response of an equalizer used to produce the equalized sequence.
Unfortunately, the above technique has a tendency to mis-correct errors, either by predicting a wrong type of error pattern among the known error patterns, or by predicting a wrong position of an error pattern within the detected codeword. Due to these mis-corrections, the above error-correction technique can have a negative impact on the performance of a communication system.